Ion-exchange polyHIPE type membrane for removing nitrate ions: Preparation, characterization, kinetics and adsorption studies

• Porous vinylbenzyl chloride/divinylbenzene polyHIPE foam was prepared.
• Trimethylamine (TMA) and triethylamine (TEA) were used to functionalize the foam.
• The presence of the organoclay improved the ion exchange capacity of the membrane.
• TEA agent increased the nitrate adsorption of the membrane more than TMA one.
• The equilibrium isotherm values were well fitted to the Freundlich isotherm model.

Highly open cellular porous vinylbenzyl chloride/divinylbenzene (VBC/DVB) polyHIPE solid foam was synthesized via polymerization of a high internal phase emulsion (HIPE). In addition, the emulsion foam was reinforced using various amounts of an organically modified montmorillonite, i.e. Cloisite30B (C30B). Scanning electron microscope (SEM) micrographs showed a typical open-cell polyHIPE structure for all the reinforced polyHIPE foams. The incorporation of only 1 wt% C30B decreased the mean cell diameter and intercellular pore size and increased the compressive mechanical properties of the copolymer foam. The amination of the neat and reinforced polyHIPE foams using an aqueous trimethylamine (TMA) solution resulted in amino-functionalized polyHIPE type membrane with nitrate anion exchange capability. The ion exchange capacity (IEC) of the resulting membranes was measured by titration procedure. The effect of the amine concentration and C30B level on the IEC of the membranes was investigated. Increasing the amination level enhanced the IEC to maximum value of 1.57 mequiv./g dry membrane. On the other hand, the increase of C30B up to 1 wt% increased the IEC value to 1.78 mequiv./g dry membrane while further increase, 3 wt%, decreased the IEC value even lower than that of the neat membrane. The prepared anion exchange polyHIPE membranes were used to remove nitrate ions from low-concentration aqueous solutions. The kinetic and thermodynamic adsorptions of nitrate ions on the membrane from the aqueous solutions were investigated. The sorption results also showed that the existence of competitive chloride and sulfate ions decreased the membrane performance for removing nitrate ions. Nevertheless, using another tertiary amine agent with bigger alkyl chain size, triethylamine (TEA), improved the selectivity of nitrate sorption to some extent in competition with the other existing interfering anions.